1. Field of the Invention
The invention relates to a scroll-type fluid displacement apparatus. More particularly, it relates to an Oldham coupling mechanism for a scroll-type refrigerant compressor, such as that used in an automotive air conditioning system.
2. Description of the Related Art
An Oldham coupling mechanism of a scroll-type fluid displacement apparatus is known in the art. For example, U.S. Pat. No. 4,655,696, issued to Utter, describes a construction of Oldham coupling mechanism of scroll-type fluid displacement apparatus. A scroll-type fluid displacement apparatus may comprise two scroll members, each having a spiral element. The scroll members maintain an angular and radial offset, so that the spiral elements interfit to form a plurality of line contacts between the spiral curved surfaces and thereby define and seal a pair of fluid pockets. During operation, the relative orbital motion of the two scroll members shifts the line contact along the spiral curved surfaces and changes the volume of the fluid pockets. Because the volume of the fluid pockets increases or decreases dependent on the direction of the orbital motion, the scroll-type fluid displacement apparatus compresses, expands or pumps fluid. An Oldham coupling prevents relative angular movement between the orbiting scroll and the fixed scroll.
An Oldham coupling mechanism also is described in Japanese Patent Publication No. H4-224,201 to Itou. Referring to FIG. 1, scroll compressor 100 includes a housing 112, having a front housing 120 and a cup-shaped casing 121 coupled to front housing 120. Compressor 100 also includes a drive shaft 113 rotatably disposed within housing 112, a fixed scroll 114 fixed to housing 112, and an orbiting scroll 115 rotatably coupled to fixed scroll 114. Orbiting scroll 115 includes a pair of first key grooves (not shown). Drive shaft 113 connects to orbiting scroll 115, so that orbiting scroll 115 orbits around the center axis of drive shaft 113.
Oldham ring 116 includes a pair of first keys (not shown) for engaging a pair of first key grooves of orbiting scroll 115 and a pair of second keys 163 which are perpendicular to the first keys. Oldham ring 116 is disposed between housing 112 and orbiting scroll 115 to prevent self-rotation of orbiting scroll 115.
Further, front housing 120 includes a front end plate 122, which is circular in shape, and a shaft housing 123, which is funnel-shaped and is secured to front end plate 122 by bolts 119. Front end plate 122 supports the axial load of orbiting scroll 115. Front end plate 122 may be made of an iron-based material, which has superior abrasion resistance. The iron-based material may be steel, steel alloy, cast iron, or cast iron alloy. Further, the wear resistance of the materials may be taken into consideration. Moreover, front housing 120 may be casted from the above materials and finished into a desired shape by a cutting process.
Front end plate 122 may be made of the iron-based material. Consequently, the iron-based material increases the weight of the fluid apparatus. Further, it is tedious to modify ferrous-based metal (iron-based material) a desired shape because ferrous-based metals have a greater hardness in comparison with non-ferrous metals. Moreover, the time consuming forming process reduces productivity with respect to front end plate 122 and increases manufacturing cost.